1. Field of the Invention
The present invention relates to a magnetic tunneling junction and its fabrication method, and more particularly, to a magnetic tunneling junction with improved electro-magnetic characteristics and thermal stability through a rapid thermal annealing.
2. Description of the Background Art
A core technology of a magnetic tunnel junction (MTJ) is a development technology of a thin film material assuming excellent and stable magnetic resistance characteristics and an integrated process technology using the conventional semiconductor circuit and process.
Tunneling magnetoresistance (TMR), that is receiving an active study, refers to a phenomenon that a tunneling current differs according to a relative magnetization direction of a ferromagnetic material in a junction with a structure of a ferromagnetic material/insulation material/ferromagnetic material structure.
The magnetic resistance thin film assuming the tunnel magnetic resistance, that is, a magnetic tunnel junction is spotlighted as a thin film device that is the most suitable for a nonvolatile magnetic random access memory (MRAM) device having excellent characteristics as well as a magnetic field sensor of a magnetic disk drive.
FIG. 1 is a sectional view of the magnetic tunnel junction, which includes: a substrate 11; a bottom lead 12; a seed layer 13; an anti-ferromagnetic layer 14; a first magnetic layer 15; a tunnel barrier layer 16; a second magnetic layer 17; and a top lead 18.
That is, the magnetic tunnel junction has a sandwich structure of the two first and second magnetic layers with the tunnel barrier 16 made as an insulation layer or an oxide layer (generally Al2O3) interposed there between.
Generally, the anti-ferromagnetic layer 14 is made of FeMn, IrMn or PtMn, or NiO.
In the device, a current flows vertically to the layers, unlike a CIP (current in plane) type giant magnetoresistance (GMR) that flows in parallel to each layer.
Accordingly, if spin directions in the magnetic layers 15 and 17 are the same (parallel to each other), resistance is low and a tunneling probability is high. If, however, the spin directions are the opposite (antiparallel to each other), resistance is high and a tunneling probability is small.
In other words, the current in the magnetic tunnel junction (referred to as a ‘tunneling current’, hereinafter) is dependent on the relative magnetization direction of the two magnetic layers 15 and 17.
Whether a corresponding bit is ‘0’ or ‘1’ can be discriminated by using the quality that the tunneling current differs (that is, a resistance value of the device differs) according to the direction of the spin. Thus, a bit can be written or read by applying a magnetic field to the magnetic tunnel junction.
The magnetic tunnel junction includes a pseudo spin-valve type in which the direction of spin can be controlled by using two magnetic layers with different coercive forces and an exchange bias type in which one of two magnetic layers is fixed through an exchange biasing field of the anti-ferromagnetic layer to thereby control a spin direction of a different magnetic layer.
In the MRAM operation, since, in most cases, one cell is selected by one of a bit line or a word line, the cells are repeatedly interfered. Thus, there is a high possibility that a magnetic creep phenomenon occurs so that a magnetization is made half or a magnetic switching is completely made.
In such a case, an error occurs in the memory device, so that it is necessary to strongly fix the magnetization by the anti-ferromagnetic layer. For this purpose, the anti-ferromagnetic layer 14 is made of a synthetic anti-ferromagnetic material (ferromagnetic layer/non-magnetic layer/ferromagnetic layer) to increase the effect of fixing the first magnetic layer 15.
In the development of the magnetic tunnel junction, one of the most important things is to increase TMR ratio because the TMR ratio is a critical factor having much influence on a density and a velocity of an MRAM device.
In addition, in the development of the magnetic tunnel junction, a magnetic switching and a thermal stability for a recording is very important.
In general, though the TMR ratio and the resistance (which is obtained by multiplying the resistivity by a junction face, R×A: R is the resistivity and A is an area of the junction face) of the magnet tunnel junction exhibit a comparatively favorable distribution in a wafer of 4˜6 inches, a magnetic field where the magnetic switching of the magnetic tunnel junction occurs is considerably uneven.
It is observed that the uneven magnetic field is more increased as the size of the magnetic tunnel junction is reduced, and especially, when the size of below 1 μm2.
The main reason for this is estimated to be a complicate magnetic switching behavior due to complicate magnetic domains and an unevenness of an infinitesimally patterned cell that is fabricated by an etching process.
In a conventional art, the magnetic tunnel junction is thermally treated for a long time while applying a magnetic field thereto, so as to improve the TMR ratio and the exchanging magnetic anisotropy: Hex) of the magnetic tunnel junction and to increase the squareness of the free layer hysteresis loop.